Distributed Temperature Sensing (DTS) has emerged as an effective technology for continuous infrastructure monitoring, providing high-resolution temperature measurements along fibre optic cables installed within dam structures and foundations. At the Mactaquac Dam near Fredericton, a DTS cable was installed within a 50 m subvertical borehole drilled into the concrete diversion sluiceway adjacent to the clay till core of the embankment dam. Spatial and temporal temperature variations along the fibre are monitored to identify anomalous changes indicative of evolving seepage conditions. The cable was installed in the concrete to avoid any possibility of damaging the embankment or introducing leakage pathways. This means that the cable is also outside the direct flow path of any seepage within the embankment or along the interface. Fibre temperatures are influenced by two other factors: (i) proximity of the borehole to vertical concrete surfaces exposed to large seasonal changes in air and water temperature, and (ii) the presence of water bearing fractures in the concrete partly caused by alkali aggregate reactivity (AAR). To address these complications, we developed an empirical approach using a decade of temperature variability to generate alerts when temporal or spatial changes exceed historical thresholds. Three temperature related parameters are continuously evaluated as a function of elevation and time: (i) temperature T(z); (ii) the vertical temperature gradient ∂𝑇/ ∂𝑧(𝑧) ; and (iii) temperature changes over time T (z). Alerts are generated when thermal behaviour exceeds historic variability, supporting proactive investigation and dam safety.